Activated carbon, adsorption filters containing activated carbon, and water purifiers

Abstract

Provided is activated carbon that is suitable for purifying drinking water or its raw water and exhibits high PFAS adsorption performance. [Solution] Activated carbon that satisfies the following (1) to (3). (1) Melanoidin decolorization performance is 50% or more and 90% or less (2) Bulk ratio is 10 cc / g or more and 100 cc / g or less (3) The specific surface area based on the N2 adsorption isotherm at -196°C is 1000 m 2 / g or more 1800m 2 / g or less

Description

[Technical Field]

[0001] The present invention relates to activated carbon, an adsorption filter containing activated carbon, and a water purifier. [Background technology]

[0002] There is a high level of concern regarding the safety and health of drinking water, and the removal of various hazardous substances is desirable. Recently, fluorinated organic compounds (PFAS), such as perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), have come to the forefront due to their adverse health effects and long-term persistence in the environment. To reduce health and environmental risks, effective April 1, 2020, a provisional target value of 50 ng / L for PFOS and PFOA in drinking water was set, and their status was changed from a "required item" to a "water quality management target setting item" (Notification No. 0330-1, dated March 30, 2020, by the Director-General for Environmental Health and Food Safety, Minister's Secretariat, Ministry of Health, Labour and Welfare, "Regarding Partial Revisions to the Ministerial Ordinance on Water Quality Standards (Enforcement Notice)").

[0003] Activated carbon, as described in Patent Document 1, has traditionally been used to purify drinking water or its raw water. When PFAS is present in drinking water or its raw water, it is desirable to remove it so that the amount is below the aforementioned target value. The use of activated carbon has also been proposed as a technology for removing PFAS from PFAS-containing water to be treated (water to be treated). For example, Patent Document 2 discloses a method for removing PFAS from a liquid or gas, the method comprising providing a first adsorbent material containing about 0.5% by weight to about 25% by weight of ions, salts, oxides, hydroxides, or carbonates of magnesium, calcium, strontium, barium, or combinations or compounds thereof, thereby increasing the adsorption capacity of the adsorbent material for PFAS relative to an adsorbent material that does not contain the ions, salts, oxides, hydroxides, or carbonates; and contacting the first adsorbent material with the PFAS-containing liquid or gas, wherein the first adsorbent material comprises one or more of carbonaceous char, activated carbon, reactivated carbon, and carbon black. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-110801 [Patent Document 2] Patent No. 7477527 Summary of the Invention [Problem to be solved by the invention]

[0005] However, while activated carbon such as that described in Patent Document 1 exhibits the ability to remove substances with small molecular sizes such as trihalomethanes, PFASs that are particularly problematic, such as PFOS, PFOA, and perfluorohexane sulfonic acid (PFHxS), all have carbon numbers of 6 to 8, which is greater than that of trihalomethanes, and therefore have large molecular sizes. Therefore, the ability of activated carbon to remove PFASs from treated water containing PFASs is insufficient.

[0006] Furthermore, methods such as those described in Patent Document 2 increase the PFAS adsorption capacity of adsorbents, such as activated carbon, which lack sufficient PFAS removal performance, by incorporating ions, salts, oxides, hydroxides, or carbonates of magnesium, calcium, strontium, barium, or combinations or compounds thereof. However, the substances incorporated here are water-soluble. Barium and many of its compounds are particularly toxic. Therefore, even if activated carbon is enriched with these substances to increase the PFAS adsorption capacity and remove PFAS from drinking water or its raw water, the treated water will still contain these eluted substances. Such water is not necessarily suitable for drinking.

[0007] In view of the above circumstances, the present invention aims to provide activated carbon, an adsorption filter, and a water purifier that are suitable for purifying drinking water or its raw water and exhibit high PFAS adsorption performance. [Means for solving the problem]

[0008] In light of the above-mentioned problems, the present inventors have conducted extensive research. As a result, they have found that activated carbons with a specific surface area within a certain range tend to have excellent adsorption performance for PFOA, a type of PFAS. They have also found that when the average pore diameter is within a specific range, PFOA adsorption performance is extremely high. They have also found that when activated carbon has a specific surface area and average pore diameter within the above ranges and exhibits decolorization performance for specific substances, it has excellent PFOA adsorption performance. The present invention was completed through further research based on these findings. [Effects of the Invention]

[0009] According to the present invention, by removing PFASs, including PFOA, from raw drinking water in advance, drinking water with a concentration below the aforementioned (provisional) target value of 50 ng / L can be easily obtained, thereby reducing health and environmental risks. Even if drinking water contains PFASs, including PFOA, it is possible to further remove PFASs, including PFOA, from the drinking water, thereby contributing to further reduction of health and environmental risks. Furthermore, the activated carbon of the present invention can also be processed into an adsorption filter containing the activated carbon. Therefore, by using the activated carbon in a water purifier containing an adsorption filter, it is possible to constantly remove PFASs, including PFOA, from drinking water, thereby contributing to reducing health and environmental risks. Furthermore, the activated carbon of the present invention can be suitably used not only for removing PFASs from drinking water or its raw water, but also for removing PFASs from untreated liquids containing PFASs or from the gas phase. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. Note that the present embodiment is an example for explaining the present invention, and the present invention is not limited to only this embodiment.

[0011] [Activated carbon] The activated carbon of this embodiment has the following physical properties (1) to (3). (1) The melanoidin decolorizing performance is 50% or more and 90% or less. (2) The bulk ratio is 10 cc / g or more and 100 cc / g or less. (3) The specific surface area based on the N2 adsorption isotherm at -196°C is 1000 m 2 / g or more 1800m 2 / g or less.

[0012] The activated carbon of this embodiment simultaneously satisfies the above physical properties (1) to (3), and therefore has excellent PFOA removal performance.

[0013] (1) Melanoidin decolorization performance The polarity of the activated carbon surface is important for efficiently removing PFOA from untreated water containing PFOA. This is because the PFOA molecule contains both a highly hydrophobic perfluoroalkyl group and a highly hydrophilic carboxyl group, which is polarized by the electron-withdrawing properties of fluorine. Therefore, if the polarity of the activated carbon surface is moderately hydrophilic, the amount of PFOA adsorbed is expected to increase due to both hydrophobic interactions with the perfluoroalkyl group and hydrogen bonding via the carboxyl group. On the other hand, if the polarity of the activated carbon surface is excessively hydrophobic or hydrophilic, electrostatic repulsion increases, resulting in a decrease in the amount of PFOA adsorbed. The polarity of the activated carbon surface can be evaluated by its adsorption performance for water-soluble pigments, such as Maillard pigments in melanoidins produced by the Maillard reaction, i.e., melanoidin decolorization performance. The activated carbon in this embodiment exhibits excellent PFOA removal performance, with a melanoidin removal performance of 50% or more, due to the contribution of hydrogen bonding via the carboxyl group in addition to the hydrophobic interaction with the perfluoroalkyl group. Furthermore, in this embodiment, the melanoidin decolorization performance is 90% or less, so the polarity of the activated carbon surface is not excessively hydrophilic, making it less likely to cause electrostatic repulsion with perfluoroalkyl groups, resulting in excellent PFOA removal performance. In this embodiment, the melanoidin decolorization performance is measured by analyzing a liquid obtained by adding a predetermined activated carbon to a melanoidin aqueous solution synthesized and adjusted in concentration under predetermined conditions using glucose and glycine as raw materials, and treating the solution at a predetermined temperature and time. Specific methods for measuring the melanoidin decolorization performance of activated carbon are described in the Examples.

[0014] Since the activated carbon of this embodiment tends to have excellent PFOA removal performance, the melanoidin decolorization performance of the activated carbon of this embodiment is preferably 52% or more, more preferably 55% or more, and is preferably 85% or less, more preferably 80% or less, and preferred ranges include 50 to 85%, 50 to 80%, 52 to 90%, 52 to 85%, 52 to 80%, 55 to 90%, 55 to 85%, and 55 to 80%.

[0015] (2) Bulk ratio In the activated carbon of this embodiment, the bulk ratio is the volume per unit weight of the activated carbon (cc / g), and increases as the micropores of the activated carbon become more developed. Activated carbon with a too high bulk ratio has insufficient development of mesopores that contribute to PFOA adsorption. However, the activated carbon of this embodiment has a bulk ratio of 100 cc / g or less, thereby exhibiting sufficient adsorption performance for PFOA. Activated carbon with a too low bulk ratio contains many spaces that do not contribute to adsorption, such as cracks and overdeveloped mesopores. However, the activated carbon of this embodiment has a bulk ratio of 10 cc / g or more, resulting in excellent PFOA removal performance due to the developed mesopores and few spaces that do not contribute to adsorption. In this embodiment, the bulk ratio is measured by crushing the activated carbon, dispersing it in water, and allowing it to settle. Specific methods for measuring the bulk ratio of activated carbon are described in the Examples.

[0016] Since the activated carbon of this embodiment tends to have excellent PFOA removal performance, the bulk ratio is preferably 12 cc / g or more, more preferably 15 cc / g or more, and is preferably 100 cc / g or less, more preferably 80 cc / g or less, and even more preferably 60 cc / g or less. Preferred ranges include 10 to 80 cc / g, 10 to 60 cc / g, 12 to 100 cc / g, 12 to 80 cc / g, 12 to 60 cc / g, 15 to 100 cc / g, 15 to 80 cc / g, and 15 to 60 cc / g.

[0017] (3) Specific surface area based on N2 adsorption isotherm at -196°C In the activated carbon of this embodiment, the specific surface area based on the N adsorption isotherm at −196° C. is an index of adsorption capacity, and the activated carbon of this embodiment has a specific surface area of ​​1000 m based on the N adsorption isotherm at −196° C. 2 / g or more, it exhibits sufficient adsorption performance for PFOA. There is no particular upper limit to the specific surface area of ​​activated carbon, but if it is too large, the yield during production will be low, so in practice, it is set to, for example, 1800 m 2 / g or less. When the specific surface area of ​​the activated carbon is in the above range, it exhibits excellent PFOA removal performance. In this embodiment, the specific surface area is determined by the BET method from the N2 adsorption isotherm at -196°C. A specific method for measuring the specific surface area of ​​the activated carbon is as described in the Examples.

[0018] Since the activated carbon of this embodiment tends to have excellent PFOA removal performance, the specific surface area based on the N adsorption isotherm at −196° C. is preferably 1100 m 2 / g or more, more preferably 1200m 2 / g or more, and preferably 1600m 2 / g or less, preferably 1550m 2 / g or less, and the preferred range is 1000 to 1600m 2 / g, 1000-1550m 2 / g, 1100-1800m 2 / g, 1100-1600m 2 / g, 1100-1550m 2 / g, 1200-1800m 2 / g, 1200-1600m 2 / g, 1200-1550m 2 / g is an example.

[0019] The activated carbon of this embodiment preferably further satisfies any one of the following physical properties (4) to (6) in addition to the physical properties (1) to (3) above. (4) The pore volume of pores with a pore diameter of 2 nm or more based on the N2 adsorption isotherm at -196°C is 0.20 mL / g or more and 2.00 mL / g or less. (5) The ratio of the pore volume of pores with a pore diameter of 2 nm or more to the pore volume of pores with a pore diameter of less than 2 nm based on an N2 adsorption isotherm at -196°C is 0.25 or more and 12.00 or less. (6) The average pore diameter based on the N2 adsorption isotherm at -196°C is 3.00 nm or more and 6.00 nm or less.

[0020] It is particularly preferable that the activated carbon of this embodiment satisfies all of the above requirements (1) to (6). Such activated carbon tends to exhibit particularly excellent PFOA removal performance.

[0021] (4) Pore volume of pores with a diameter of 2 nm or more based on the N2 adsorption isotherm at -196°C For activated carbon to exhibit superior PFOA adsorption performance, it is preferable that the pore volume of pores with an appropriate pore diameter is large. In the activated carbon of this embodiment, when the pore volume of pores with a pore diameter of 2 nm or more based on the N2 adsorption isotherm at -196°C is 0.20 mL / g or more, the activated carbon exhibits even higher adsorption performance for PFOA. There is no particular upper limit for the pore volume of pores with a pore diameter of 2 nm or more in activated carbon, but if the pore volume is too large, the production yield will be low, so in practice, it is preferably 2.00 mL / g or less. In this embodiment, the pore volume is calculated by the BJH method from the N2 adsorption isotherm at -196°C. Specific methods for measuring the pore volume are as described in the Examples.

[0022] Since the activated carbon of this embodiment tends to exhibit better PFOA removal performance, the pore volume of pores having a pore diameter of 2 nm or more based on the N adsorption isotherm at −196° C. of the activated carbon of this embodiment is preferably 0.20 mL / g or more, more preferably 0.22 mL / g or more, and even more preferably 0.24 mL / g or more, and is also preferably 2.00 mL / g or less, more preferably 1.98 mL / g or less, and even more preferably 1.96 mL / g or less, and preferred ranges include 0.20 to 2.00 mL / g, 0.20 to 1.98 mL / g, 0.20 to 1.96 mL / g, 0.22 to 2.00 mL / g, 0.22 to 1.98 mL / g, 0.22 to 1.96 mL / g, 0.24 to 2.00 mL / g, 0.24 to 1.98 mL / g, and 0.24 to 1.96 mL / g.

[0023] (5) The ratio of the pore volume of pores with a diameter of 2 nm or more to the pore volume of pores with a diameter of less than 2 nm based on the N2 adsorption isotherm at -196°C For activated carbon to have better PFOA removal performance, it is preferable that the pore volume of pores with diameters ineffective for PFOA adsorption be small. This can be expressed as the ratio of the pore volume of pores with diameters effective for PFOA adsorption, i.e., pores with diameters of 2 nm or more, to the pore volume of pores with diameters ineffective for PFOA adsorption, i.e., pores with diameters less than 2 nm. When this ratio is equal to or greater than a certain value, the activated carbon has better PFOA removal performance. In the activated carbon of this embodiment, when this ratio based on the N2 adsorption isotherm at -196°C is 0.25 or greater, the pore volume of pores with diameters ineffective for PFOA adsorption is sufficiently small, thereby exhibiting better PFOA removal performance. The upper limit of this ratio is not particularly limited, but since a ratio that is too large tends to result in low production yields, in practice it is, for example, 12.00 or less. In this embodiment, the pore volume is calculated by the BJH method from the N2 adsorption isotherm at -196°C. Specific methods for measuring the pore volume are as described in the Examples.

[0024] Since the activated carbon of this embodiment tends to have better PFOA removal performance, the ratio of the pore volume of pores with a pore diameter of 2 nm or more to the pore volume of pores with a pore diameter of less than 2 nm based on the N2 adsorption isotherm at -196°C of the activated carbon of this embodiment is preferably 0.25 or more, more preferably 0.50 or more, even more preferably 0.70 or more, and is preferably 12.00 or less, more preferably 11.50 or less, even more preferably 11.00 or less, and preferred ranges include 0.25 to 12.00, 0.25 to 11.50, 0.25 to 11.00, 0.50 to 12.00, 0.50 to 11.50, 0.50 to 11.00, 0.70 to 12.00, 0.70 to 11.50, and 0.70 to 11.00.

[0025] (6) Average pore diameter based on N2 adsorption isotherm at -196°C Furthermore, in order for activated carbon to have better PFOA removal performance, it is preferable that the pore diameter of the activated carbon is compatible with the molecular size of PFOA. The average pore diameter of the activated carbon in this embodiment, based on the N adsorption isotherm at −196°C, is preferably 3.0 nm or more. The activated carbon according to this embodiment, having an average pore diameter of 3.00 nm or more, is more compatible with the molecular size of PFOA, a compound with eight carbon atoms, and exhibits better removal performance. The upper limit of the average pore diameter of the activated carbon is not particularly limited, but since an activated carbon that is too large reduces the production yield, in practice it is, for example, 6.00 nm or less. By having the average pore diameter within the above range, the activated carbon has pores with a pore diameter more compatible with the molecular size of PFOA, and tends to exhibit better PFOA removal performance. In this embodiment, the average pore diameter is calculated by the BET method from the N adsorption isotherm at −196°C. Specific methods for measuring the average pore diameter are as described in the Examples.

[0026] Since the activated carbon of this embodiment tends to have better PFOA removal performance, the average pore diameter based on the N adsorption isotherm at -196 ° C. of the activated carbon of this embodiment is preferably 3.00 nm or more, more preferably 3.05 nm or more, and even more preferably 3.10 nm or more, and is preferably 6.00 nm or less, more preferably 5.85 nm or less, even more preferably 5.70 nm or less, and even more preferably 3.70 nm or less. Preferred ranges include 3.00 to 6.00 nm, 3.00 to 5.85 nm, 3.00 to 5.70 nm, 3.00 to 3.70 nm, 3.05 to 6.00 nm, 3.05 to 5.85 nm, 3.05 to 5.70 nm, 3.05 to 3.70 nm, 3.10 to 6.00 nm, 3.10 to 5.85 nm, 3.10 to 5.70 nm, and 3.10 to 3.70 nm.

[0027] [Activated carbon fiber] The shape of the activated carbon of this embodiment is not particularly limited, and examples thereof include powder, granules, pellets, and fibers. For example, fibrous activated carbon, which is activated carbon in the form of fibers, is suitably used in water purifiers, and the fibrous activated carbon of this embodiment satisfies the physical properties (1) to (3) above and exhibits superior PFOA removal performance. In this embodiment, in order to form the activated carbon in the form of fibers, the raw material of the activated carbon is spun and molded into a fibrous shape. For specific methods, see the description of the Examples.

[0028] (7) Tensile strength The fibrous activated carbon of this embodiment preferably further satisfies the physical property requirement (7) below. (7) The tensile strength is 0.05 GPa or more and 0.25 GPa or less.

[0029] When the activated carbon of this embodiment is a fibrous activated carbon, the fibrous activated carbon preferably satisfies all of the above requirements (1) to (7). Such a fibrous activated carbon of this embodiment tends to exhibit better PFOA removal performance.

[0030] The tensile strength of the fibrous activated carbon of this embodiment is preferably 0.05 GPa or more and 0.25 GPa or less. A tensile strength of 0.05 GPa or more makes the activated carbon less susceptible to breakage during use or processing into an adsorption filter, and even pores effective for PFOA adsorption are less likely to be destroyed, which tends to make it easier to maintain excellent PFOA removal performance. If the tensile strength is 0.25 GPa or less, the fibrous activated carbon has sufficient pores within it that allow fluids such as water to penetrate, increasing the contact efficiency between the surface of the fibrous activated carbon and the fluid, which tends to result in better PFOA removal performance. In this embodiment, the tensile strength is measured according to the method specified in JIS K 1477:2007, "Test Method for Fibrous Activated Carbon, 7.3.2 Tensile Strength." A specific method for measuring the tensile strength of the fibrous activated carbon is as described in the Examples.

[0031] [Activated carbon manufacturing method] The method for producing the activated carbon of this embodiment is not particularly limited as long as it is a method that can produce activated carbon that satisfies the physical properties (1) to (3) above, but the following production method is preferred. (Method of producing activated carbon of the present invention) The method includes a molding step of molding a raw material for the activated carbon, a stabilization step of stabilizing the molded product obtained in the molding step, and an activation step of activating the carbonaceous material obtained in the stabilization step, the raw material of the activated carbon contains an yttrium compound; In the infusible step, the atmosphere temperature is raised to 360 to 400°C to make the material infusible, The activation step is a step of activating the catalyst at an atmospheric temperature of 930 to 950°C for 30 to 40 minutes, A method for producing activated carbon, wherein in the activation step, steam is supplied so that the amount of steam is 500 to 600 parts by mass (500 parts by mass or more and 600 parts by mass or less) per 100 parts by mass of the carbonaceous material obtained in the infusibilization step. The above manufacturing method will be described in detail below.

[0032] [Raw materials] The raw material for activated carbon is not particularly limited as long as it can be molded into any shape and then infusibilized to produce a carbonaceous material, and examples thereof include plants such as coconut shells and wood flour, fossil fuel-derived products such as coal pitch and petroleum pitch, synthetic resins such as polyacrylonitrile resin and phenolic resin, and natural fibers such as cellulose and its derivatives. Of these, plants such as coconut shells and wood flour and fossil fuel-derived products such as coal pitch and petroleum pitch are preferred, with coal pitch or petroleum pitch being more preferred, and coal pitch being even more preferred. These raw materials may be used alone, or two or more types may be mixed together as needed.

[0033] [Molding process] The activated carbon is preferably obtained through a molding process in which raw materials for the activated carbon are molded. In the molding process, by converting the raw materials into a lump, pellet, or fiber form rather than leaving them in a powder or liquid state, a carbonaceous material can be more suitably obtained in the infusibilization process described below. The molding method is not particularly limited as long as it can mold the raw materials into the desired shape. For example, for a lump, a mixing and kneading method using a Henschel mixer or a kneading method using a batch or continuous kneader can be used; for a pellet, an extrusion molding method using a front extruder, a bottom extruder, or a disk pelletizer can be used; and for a fiber, a spinning method such as solution spinning or melt spinning can be used.

[0034] In the method for producing activated carbon of the present invention, the raw material for the activated carbon contains an yttrium compound. When gas activation is performed using water vapor, the yttrium compound acts as an activation aid that facilitates the formation of relatively large pores. This makes it easier to control the amount of water vapor relative to the carbonaceous material in the activation step described below so that the properties (2) and (3), or (2) to (6), are satisfied. Furthermore, by setting the amount of water vapor relative to the carbonaceous material in the activation step described below within a specific range, the property (1) is more likely to be satisfied, making it easier to obtain activated carbon that exhibits excellent PFOA removal performance.

[0035] Examples of yttrium compounds include inorganic yttrium compounds such as yttrium oxide, yttrium hydroxide, yttrium halide, and yttrium sulfate; organic yttrium acid salts such as yttrium acetate; and organic yttrium compounds. Among these yttrium compounds, organic yttrium compounds are preferred from the viewpoint of increasing the dispersibility of the yttrium compound in the activated carbon precursor and making it easier for the resulting activated carbon to satisfy the physical properties (2) and (3), or (2) to (6), within suitable ranges. A preferred example of an organic yttrium compound is an yttrium complex having a β-diketone compound as a ligand. Examples of β-diketone compounds include those having the structures shown in the following formulas (1) to (3).

[0036] [ka]

[0037] In the formula (1), R 12 and R 13 are the same or different and represent an alkyl group having 1 to 22 carbon atoms or an alkenyl group having 1 to 22 carbon atoms, preferably an alkyl group having 1 to 11 carbon atoms or an alkenyl group having 1 to 11 carbon atoms, more preferably an alkyl group having 1 to 8 carbon atoms, and even more preferably a methyl group. In the formula (1), R11 represents a hydrogen atom, an alkyl group having 1 to 22 carbon atoms or an alkenyl group having 1 to 22 carbon atoms, preferably a hydrogen atom, an alkyl group having 1 to 11 carbon atoms or an alkenyl group having 1 to 11 carbon atoms, and more preferably a hydrogen atom.

[0038] In the formula (2), R 21 represents a hydrogen atom, an alkyl group having 1 to 22 carbon atoms, or an alkenyl group having 1 to 22 carbon atoms, preferably a hydrogen atom, an alkyl group having 1 to 11 carbon atoms, or an alkenyl group having 1 to 11 carbon atoms, more preferably a hydrogen atom. 22 represents a hydrogen atom, an alkyl group having 1 to 22 carbon atoms, or an alkenyl group having 1 to 22 carbon atoms, preferably a hydrogen atom, an alkyl group having 1 to 11 carbon atoms, or an alkenyl group having 1 to 11 carbon atoms, more preferably a hydrogen atom. 23 represents an alkyl group having 1 to 22 carbon atoms or an alkenyl group having 1 to 22 carbon atoms, preferably an alkyl group having 1 to 11 carbon atoms or an alkenyl group having 1 to 11 carbon atoms, more preferably an alkyl group having 1 to 8 carbon atoms, and even more preferably a methyl group.

[0039] In the formula (3), R 31 and R 33 are the same or different and represent a hydrogen atom, an alkyl group having 1 to 22 carbon atoms, or an alkenyl group having 1 to 22 carbon atoms, preferably a hydrogen atom, an alkyl group having 1 to 11 carbon atoms, or an alkenyl group having 1 to 11 carbon atoms, more preferably a hydrogen atom. 32represents a hydrogen atom, an alkyl group having 1 to 22 carbon atoms or an alkenyl group having 1 to 22 carbon atoms, preferably a hydrogen atom, an alkyl group having 1 to 11 carbon atoms or an alkenyl group having 1 to 11 carbon atoms, more preferably a hydrogen atom.

[0040] Among the yttrium complexes having a β-diketone type compound as a ligand, the yttrium complex having a β-diketone type compound represented by the formula (1) as a ligand is preferred, and more preferred is trisacetylacetonatoyttrium [acetylacetone (R in the formula (1)] 11 and R 13 is a methyl group, R 12 (compounds in which each atom is a hydrogen atom) and an yttrium complex in which three molecules are coordinated.

[0041] In the method for producing activated carbon of the present invention, the parts by mass of the yttrium compound per 100 parts by mass of the raw material for activated carbon is preferably 0.5 to 2.0 parts by mass, more preferably 1.0 to 1.5 parts by mass.

[0042] [Infusible process] Activated carbon production involves a stabilization step after the molding step. When the melting point of the raw material is low, the molded product obtained in the molding step can be converted into a carbonaceous material by the stabilization step, and then, through the activation step, activated carbon with excellent PFOA removal performance can be obtained. In the stabilization step, the temperature is raised from room temperature (20-30°C) to an ambient temperature of 360-400°C for stabilization (hereinafter, the maximum ambient temperature reached by this temperature increase may be referred to as the "ultimate ambient temperature"). Stabilization at this ultimate ambient temperature makes it easier to control the amount of water vapor relative to the carbonaceous material in the activation step described below so that it satisfies the physical properties (2) and (3), or (2) to (6), even if the amount of water vapor relative to the carbonaceous material is within a specific range. The atmosphere used in the stabilization step may be a known one, and examples include stabilization in an atmosphere containing an oxidizing gas such as oxygen. The time required to raise the temperature to the ultimate ambient temperature is preferably about 55-65 minutes.

[0043] [Activation process] In the method for producing activated carbon of the present invention, the activation step is a step of gas activation using water vapor as an activation gas at an atmospheric temperature of 930 to 950°C for 30 to 40 minutes, and in this activation step, water vapor is supplied so that the amount of water vapor is 500 to 600 parts by mass (500 to 600 parts by mass) per 100 parts by mass of the carbonaceous material obtained in the infusibilization step. By performing activation at such an atmospheric temperature and for such an activation time, it becomes easier to control the amount of water vapor so that the properties (2) and (3) or (2) to (6) above are satisfied. Furthermore, by setting the amount of water vapor in this range, it becomes easier to make the polarity of the activated carbon surface appropriately hydrophilic, making it easier to satisfy the property (1) above, and as a result, it becomes easier to obtain activated carbon that exhibits excellent PFOA removal performance.

[0044] The activated carbon obtained by the activation step can be used as is, or it can be washed and dried as necessary before use. Washing is preferred for use in liquid-phase applications, and can be performed by water washing or acid washing. Acid washing is more preferred, as this removes the bound activation aid and metal salts in the raw materials from the surface functional groups on the activated carbon, making the surface functional groups more likely to form polar interactions with PFOA, which tends to more favorably produce activated carbon with excellent PFOA removal performance. The acid used for acid washing is not particularly limited, and mineral acids such as hydrochloric acid and sulfuric acid, and organic acids such as acetic acid, propionic acid, and oxalic acid can be used. Of these, mineral acids such as hydrochloric acid and sulfuric acid are preferred, and sulfuric acid is more preferred. When yttrium is used as the activation aid, the yttrium content of the activated carbon obtained by washing can be 10 mg / kg or less, preferably less than 1 mg / kg, and more preferably less than 0.1 mg / kg. The yttrium content of the activated carbon is calculated from the amount of yttrium element measured by an ICP emission spectrometer. The specific measurement method is as described in the Examples.

[0045] [Application] The activated carbon of this embodiment exhibits excellent PFOA removal performance and can be used to remove PFAS from drinking water or its raw water. Furthermore, it can be suitably used in various other applications requiring PFAS removal. Examples of such applications include water purifiers, wastewater treatment, waste oil treatment, oil and fat refining, air purifiers, and gas removal.

[0046] More specifically, activated carbon is suitable for applications requiring PFAS removal, including: 1) Water Purifier: Household water purifier element; Industrial water purifier element. 2) Wastewater treatment: industrial wastewater discharged from factories and businesses, as well as agricultural wastewater; contaminated groundwater, leachate from waste disposal sites, industrial wastewater containing PFAS, wastewater containing PFAS, and rivers, lakes, and other areas. 3) Waste oil treatment: Wastewater, waste liquids, and waste food containing oils and lard such as vegetable oils (e.g., rapeseed oil, sesame oil, soybean oil, corn oil, palm oil, olive oil, and peanut oil), animal oils (e.g., butter and lard), and processed oils (e.g., margarine), which are discharged from ordinary households, commercial kitchens, and buildings, as well as from public sewage and wastewater treatment facilities. 4) Oil and fat refining: vegetable oils, animal oils, processed oils, and lard. 5) Air purifiers: household air filters and industrial air filters. 6) Gas adsorption: PFAS and volatile fluorine compounds generated during the decomposition process of PFAS.

[0047] [Device] The device of this embodiment includes the activated carbon of this embodiment. The function of the activated carbon of this embodiment is utilized by an apparatus containing the same. The apparatus of this embodiment is preferably a treatment apparatus. In this specification, the term "treatment apparatus" is not particularly limited as long as it is an apparatus that can remove or treat substances to be removed contained in treatment targets such as wastewater, waste liquid, and oil using the activated carbon of this embodiment. Examples of such treatment apparatus include apparatuses that include adsorption filters, columns, tanks or baths, tubes, cartridges, cylinders, and sheets containing activated carbon (hereinafter also simply referred to as "filters, etc. containing activated carbon"), and filtration apparatuses.

[0048] Substances to be removed include, but are not limited to, PFAS.

[0049] Examples of filtration devices include cartridge-type filtration devices (water purifiers) containing activated carbon, membrane treatment devices, and ultrafiltration membrane devices.

[0050] The treatment device may be equipped with other adsorption filters in addition to the activated carbon-containing filter, etc. Examples of such other adsorption filters include metal filters made of stainless steel, aluminum, bronze, copper, titanium, nickel, etc., and resin filters made of polypropylene, polyvinyl chloride, polyvinylidene chloride, polyethylene, polyamide, fluorine-based resin, etc.

[0051] The treatment equipment may be of either a batch or continuous type, and activated carbon may be used in either type. [Example]

[0052] EXAMPLES The present invention will be explained in more detail below by showing examples and comparative examples, but the present invention is not limited to these examples in any way.

[0053] [Evaluation method] (Melanoidin decolorization performance) The melanoidin used in the test was prepared by preparing an aqueous solution containing 1 mol / L glucose, 1 mol / L glycine, and 0.1 mol / L sodium bicarbonate. The solution was heated at 120°C for 1 hour in an autoclave to obtain a 1000 mg / L aqueous solution. The test solution was used as the test solution. The absorbance (C0) of this test solution at 430 nm was measured using a UV-visible spectrophotometer (JASCO Corporation, UV-visible spectrophotometer V-650 (trade name)). 2.0 g of activated carbon was added to 1 L of the test solution, and the mixture was shaken at 25°C for 24 hours. The activated carbon was then filtered off to obtain a treated solution. The absorbance (C0) of this treated solution at 430 nm was measured using a UV-visible spectrophotometer (JASCO Corporation, UV-visible spectrophotometer V-650 (trade name)). The melanoidin decolorization performance was calculated using equation (1). Melanoidin decolorization performance (%) = 100 × (C0-C) / C0(1)

[0054] (bulk ratio) The bulk ratio of activated carbon was measured as follows. First, 250 mL of pure water was placed in a mixer (Zojirushi Corporation, BM-SA10 (model)), and 3 g of activated carbon from each of the examples and comparative examples was added and pulverized for 20 seconds. This pulverized product was poured into a 500 mL measuring cylinder together with water, and further water was added to make a 500 mL suspension. This was left to stand for 30 minutes to allow the activated carbon to settle, and the volume (cc) of the activated carbon layer was measured. This volume was divided by 3, which is the weight of the activated carbon added, to obtain the bulk ratio (cc / g) of the activated carbon.

[0055] (average pore diameter, total pore volume and specific surface area) The average pore diameter, total pore volume, and specific surface area were calculated based on a nitrogen adsorption isotherm at -196°C. Specifically, the nitrogen adsorption isotherm was prepared as follows. The activated carbon sheet was cooled to -196°C (the boiling point of nitrogen), and nitrogen gas was introduced to measure the nitrogen gas adsorption amount V [cc / g] by the volumetric method. The pressure P [hPa] of the introduced nitrogen gas was gradually increased, and the value obtained by dividing the value by the saturated vapor pressure P [hPa] of the nitrogen gas was defined as the relative pressure (P / P). A nitrogen adsorption isotherm was prepared by plotting the adsorption amount against each relative pressure. The nitrogen gas adsorption amount was measured using a commercially available automatic gas adsorption amount measurement device (trade name "AUTOSORB-6" (manufactured by Anton Paar)). The nitrogen adsorption isotherm was prepared and analyzed using the analysis program provided with the device. The total pore volume (A, unit: mL / g) was calculated based on the adsorption capacity at P / P = 0.995 based on the nitrogen adsorption isotherm. The specific surface area (B, unit m 2 The specific surface area (P / P) was calculated from a line obtained by the multipoint BET method based on the nitrogen adsorption isotherm in the relative pressure region P / P = 0.00 to 0.10. The average pore diameter was calculated from the values ​​of A and B using formula (2). Average pore diameter (nm) = 4 × A / B × 1000 (2)

[0056] (Pore volume of pores with a diameter of 2 nm or more and the ratio of the pore volume of pores with a diameter of 2 nm or more to the volume of pores with a diameter of less than 2 nm) The pore volume (mL / g) of activated carbon pores with a diameter of 2 nm or greater was determined by the BJH method from the N adsorption isotherm at -196 °C. Specifically, the nitrogen adsorption isotherm used in calculating the average pore diameter, total pore volume, and specific surface area was used to obtain a curve by BJH analysis in the relative pressure range P / P = 0.385 to 0.99. From the obtained curve, the cumulative pore volume for pores of each pore diameter was calculated, and the cumulative pore volume (C, in mL / g) of pores with a diameter of up to 2.00 nm was obtained. The pore volume (D, in mL / g) of pores with a diameter of 2.00 nm or greater was calculated by subtracting C from the total pore volume (A) described above. The ratio of the pore volume of pores with a diameter of 2 nm or greater to the pore volume of pores with a diameter of less than 2 nm was calculated by dividing D by C.

[0057] (tensile strength) The tensile strength of the fibrous activated carbon was measured by first measuring the fiber diameter in accordance with JIS K 1477:2007 7.3.1, Method a, using a laser diameter measuring instrument (Anritsu Corporation, M550A (model)). The tensile strength was measured in accordance with JIS K 1477:2007 7.3.2, using a tensile tester (Shimadzu Corporation, SIMADZU EZ-EX (model)). The tensile strength was calculated from the fiber diameter and the tensile strength.

[0058] (PFOA removal performance) The instrument settings for analysis and quantification, the preparation of calibration standard solutions and calibration curves, and the analytical methods all conformed to the methods described in the Ministry of the Environment's "Enforcement of Environmental Standards for the Protection of Human Health in Relation to Water Pollution (Notice) (May 28, 2020, Kansui Daisui-hatsu No. 2005281 and Kansui Daido-hatsu No. 2005282)." A perfluorooctanoic acid standard (AccuStandard, 100 μg / mL methanol solution) was diluted with ultrapure water to a concentration of 50 μg / L, which was used as the test solution. Activated carbon was first crushed for 1 minute and 30 seconds per 1.5 g using a high-speed vibration sample crusher (CMT Corporation, HEIKO Sample Mill, Model TI-100). A predetermined amount of crushed activated carbon was added to 100 mL of test solution, and the solution was shaken at a frequency of 148 rpm and a thermostatic bath temperature of 25°C until adsorption equilibrium was reached. The activated carbon was then filtered off, and the filtrate was analyzed by a liquid chromatography mass spectrometer (Agilent). The residual PFOA concentration in the filtrate was quantified using a 1200 series / 6130 (manufactured by AIST Technologies). The difference between the PFOA concentration in the test solution and the residual PFOA concentration in the filtrate was divided by the weight of the added activated carbon to calculate the amount of PFOA adsorbed per unit weight of activated carbon. This was performed under three conditions for each of the activated carbons of the Example and Comparative Examples, varying the amount of activated carbon added. Using Freundlich's adsorption isotherm, the amount of PFOA adsorbed per unit weight of activated carbon was plotted on the vertical axis against the residual PFOA concentration in the filtrate on the horizontal axis to create an adsorption isotherm for each activated carbon. From the adsorption isotherm, the amount of PFOA adsorbed per unit weight of activated carbon (μg / mg-AC) when the residual PFOA concentration reached 10 μg / L was calculated, and this value was used as the PFOA removal performance of the activated carbon.

[0059] (PFOA concentration after distribution of 50ng / L treated water) The 50ng / L post-treatment PFOA concentration was measured using a PFOA filtration capacity test under conditions conforming to JWPAS B. Specifically, the test solution described above was diluted 1000 times with ultrapure water to prepare 50ng / L treatment water. Each sample was packed into a 15mm inner diameter column to a height of 38mm, and the treatment water was passed through at a flow rate of 0.33L / min. The PFOA concentration of the filtrate collected after 100L had passed was measured using the analytical method described above, and this was recorded as the 50ng / L post-treatment PFOA concentration in the filtrate.

[0060] (Yttrium content of activated carbon) First, the activated carbon raw material or activated carbon was dried at 110 ° C for 2 hours, and then 4.0 g (referred to as A (g)) was weighed and placed in a 300 mL beaker. 180 mL of pure water and 0.1 mL of nitric acid + water (1 + 99) were added, and the mixture was boiled for 10 minutes. After 10 minutes, pure water was added to make 200 mL. This was filtered using No. 5C filter paper, and 100 mL of the resulting filtrate was transferred to a beaker and heated and concentrated to 10 mL. 1 mL of nitric acid was added, and the volume was adjusted to 20 mL with pure water. The resulting test solution was diluted with a dilution factor B as necessary, and the yttrium concentration in the solution, C (mg / L), was measured using an ICP emission spectrometer (Varian, Model 715-ES). The yttrium content in the sample (mg / kg) was calculated using the following formula: {B×C×(20 / 100)×200}÷A The calibration curve for ICP atomic emission spectrometry was prepared using an yttrium standard solution of 1 mg Y / mL (1000 ppm).

[0061] [Example 1] The activated carbon raw material was a mixture of 100 parts by mass of coal pitch and 1.3 parts by mass of tris(acetylacetonato)yttrium(III) (manufactured by Takanami Inorganic Co., Ltd.) as an activation aid. The fibers were formed using a melt spinning machine (manufactured by Nippon Steel Corporation) and deposited to a thickness of approximately 10 cm to form a mat. This mat was then continuously processed by moving it from a conveyor furnace (manufactured by Osaka Gas Engineering Co., Ltd.) for the stabilization process to a conveyor furnace (manufactured by Koyo Thermo Systems Co., Ltd.) for the activation process. The stabilization process involved heating the material while moving it from the inlet to the outlet in the conveyor furnace (manufactured by Osaka Gas Engineering Co., Ltd.). Oxygen was present as an oxidizing gas at a partial pressure of 21%, and the temperature of the conveyor furnace was controlled so that the ambient temperature increased stepwise from room temperature at the inlet to 370°C at the outlet. The stabilization was performed over a 60-minute period. The activation step was performed in a conveyor furnace (manufactured by Koyo Thermo Systems Co., Ltd.) by heating the material while moving it from the inlet to the outlet. Steam was supplied as an activation gas to the conveyor furnace in a range of 550±50 parts by mass per 100 parts by mass of the raw material. The gas was then moved to the outlet and retained there for 32 minutes at an atmospheric temperature of 940°C, whereupon activation was performed and the material was cooled. The activated carbon obtained was washed with sulfuric acid to remove the activation aid, and then dried to obtain the activated carbon of Example 1. The yttrium content of the activated carbon was measured by the above-mentioned method, and no yttrium was detected (less than 0.1 mg / kg). This means that the yttrium compound, which is the activation aid, was removed by the sulfuric acid washing.

[0062] [Example 2] A fibrous activated carbon of Example 2 was obtained in the same manner as in Example 1, except that the atmospheric temperature of the conveyor furnace in the activation step was set to 930°C. When the yttrium content of the activated carbon was measured by the above-mentioned method, no yttrium was detected (less than 0.1 mg / kg). In other words, the yttrium compound, which is an activation aid, was removed by the above-mentioned sulfuric acid washing.

[0063] [Example 3] A fibrous activated carbon of Example 3 was obtained in the same manner as in Example 1, except that the atmospheric temperature of the conveyor furnace in the activation step was set to 950°C. When the yttrium content of the activated carbon was measured by the above-mentioned method, no yttrium was detected (less than 0.1 mg / kg). In other words, the yttrium compound, which is an activation aid, was removed by the above-mentioned sulfuric acid washing.

[0064] [Comparative Example 1] A fibrous activated carbon of Comparative Example 1 was obtained in the same manner as in Example 1, except that the atmospheric temperature of the conveyor furnace in the activation step was set to 890°C. When the yttrium content of the activated carbon was measured by the above-mentioned method, no yttrium was detected (less than 0.1 mg / kg). In other words, the yttrium compound, which is an activation aid, was removed by the above-mentioned sulfuric acid washing.

[0065] Comparative Example 2 The fibrous activated carbon of Comparative Example 2 was obtained in the same manner as in Example 1, except that no activation aid was used, the movement time in the conveyor furnace in the infusible step was 55 minutes, steam was supplied from the middle of the furnace toward the outlet side in a range of 650±50 parts by mass per 100 parts by mass of raw material, the ambient temperature of the conveyor furnace in the activation step was 900°C, and the material was moved to the outlet over 30 minutes.

[0066] Comparative Example 3 The fibrous activated carbon of Comparative Example 3 was obtained in the same manner as in Example 1, except that no activation aid was used, the movement time in the conveyor furnace in the infusible step was 55 minutes, steam was supplied from the middle of the furnace toward the outlet side in a range of 650±50 parts by mass per 100 parts by mass of raw material, the ambient temperature of the conveyor furnace in the activation step was 950°C, and the material was moved to the outlet over 30 minutes.

[0067] Comparative Example 4 The fibrous activated carbon of Comparative Example 4 was obtained in the same manner as in Example 1, except that no activation aid was used, the ultimate ambient temperature, which is the temperature at the end of the conveyor furnace in the stabilization step, was set to 375°C, the travel time in the stabilization step was 72 minutes, steam in the activation step was supplied from the middle of the furnace toward the outlet so that the amount was in the range of 1250±50 parts by mass per 100 parts by mass of raw material, the ambient temperature of the conveyor furnace in the activation step was set to 950°C, and the material was transported to the outlet over 40 minutes.

[0068] Comparative Example 5 The fibrous activated carbon of Comparative Example 5 was obtained in the same manner as in Example 1, except that no activation aid was used, the ultimate ambient temperature, which is the temperature at the end of the conveyor furnace in the stabilization step, was set to 365°C, the travel time in the stabilization step was 78 minutes, steam in the activation step was supplied from the middle of the furnace toward the outlet so that the amount of steam was in the range of 2050±50 parts by mass per 100 parts by mass of raw material, the ambient temperature of the conveyor furnace in the activation step was set to 950°C, and the material was transported to the outlet over 40 minutes.

[0069] [Evaluation results] The melanoidin decolorization performance, bulk ratio, specific surface area, total pore volume, pore volume of pores with a pore diameter of 2 nm or more, the ratio of the pore volume of pores with a pore diameter of 2 nm or more to the pore volume of pores with a diameter of less than 2 nm, average pore diameter, tensile strength, and PFOA removal performance of the activated carbons obtained in Examples 1 to 3 and Comparative Examples 1 to 5 are summarized in Table 1. As shown in Table 1, the activated carbons of Examples 1 to 3 were superior in PFOA removal performance to the activated carbons of Comparative Examples 1 to 5.

[0070] [Table 1]

Claims

1. Activated carbon that satisfies all of the following (1) to (6): (1) Melanoidin decolorization performance is 50% or more and 90% or less (2) Bulk ratio of 10 cc / g or more and 100 cc / g or less (3) N at -196°C 2 The specific surface area based on the adsorption isotherm is 1200 m 2 / g or more 1800m 2 / g or less (4) The pore volume of pores having a diameter of 2 nm or more based on the N 2 adsorption isotherm at −196° C. is 0.20 mL / g or more and 2.00 mL / g or less. (5) The ratio of the pore volume of pores having a diameter of 2 nm or more to the pore volume of pores having a diameter of less than 2 nm based on the N 2 adsorption isotherm at −196° C. is 0.25 or more and 12.00 or less. (6) An average pore diameter based on the N 2 adsorption isotherm at −196° C. of 3.10 nm or more and 6.00 nm or less

2. The fibrous activated carbon according to claim 1 , which is in the form of a fiber.

3. The fibrous activated carbon according to claim 1 or 2, further satisfying the following (7): (7) Tensile strength of 0.05 GPa or more and 0.25 GPa or less

4. A method for producing activated carbon, comprising: The method includes a molding step of molding a raw material for the activated carbon, a stabilization step of stabilizing the molded product obtained in the molding step, and an activation step of activating the carbonaceous material obtained in the stabilization step, the raw material of the activated carbon contains an yttrium compound; In the infusible step, the atmosphere temperature is raised to 360 to 400°C to make the material infusible, The activation step is a step of activating the mixture at an atmospheric temperature of 930 to 950°C for 30 to 40 minutes, The method for producing activated carbon according to claim 1, wherein in the activation step, water vapor is supplied in an amount of 500 to 600 parts by mass (500 parts by mass or more and 600 parts by mass or less) per 100 parts by mass of the carbonaceous material obtained in the infusibilization step.

5. An adsorption filter comprising the activated carbon of claim 1.

6. A water purifier comprising the adsorption filter of claim 5.

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